For the purpose of centering or positioning the spindle of a machine tool such as a milling machine, a radial cutting machine or a drilling machine, a spindle equipped with a centering microscope is commonly used, and the surface of the work is observed under the microscope and a cross-mark in the field of vision is matched with a mark on the work.
According to this method, however, an expensive special microscope has to be provided for the sole purpose of centering or positioning the spindle and work relative to each other; skill and experience are required for using the microscope; and it takes a relatively long time for centering or positioning the spindle. This is detrimental to efficiency of the machining operation. Moreover, the use of an optical instrument for centering or positioning is likely to produce an error due to the instrument itself. Furthermore, for mahining work with a high precision, a correspondingly high precision machine tool and accessories are needed. Thus, not only is the cost of the machine tool increased, but also the cost of the product is increased.
The sole use of a conventional centering device is for centering, and after centering or positioning is achieved, the whole device including a centering needle fixed thereto has to be removed from the spindle chuck of the machine tool and thereafter a cutting tool has to be fitted into the chuck for the machining operation.
Thus, a centering device which can function only as such has limited applicability. When the centering device is exchanged for a cutting tool after centering has been achieved, the tool to be used is not always fitted into the chuck in the same position as the centering device; and accordingly a miscentering which occurs during fitting the tool into the chuck cannot be corrected. For this reason there has been a keenly felt need for development of a new centering device which has a simplified construction, is inexpensive to manufacture and can be readily and easily used for high precision centering.